Homeland security has become of more than passing interest. One aspect of security involves surveillance of regions near borders to be protected from invasion, whether the invasion is (a) by hostile troops seeking to enter and attack a region to be protected or'(b) by undocumented or criminal persons, as might occur at the U.S.-Mexican border. One of the problems with such surveillance is that the regions under surveillance may be large, and the manpower available to perform the surveillance may be small. The availability of personnel to counter a detected incursion is a different issue. When the number of eyes available to perform surveillance or to survey is small, there is the possibility, or even the likelihood, that some incursions will not be noticed. Even when a large number of eyes is available, the relative infrequency of incursions may lead to momentary inattention, which again can lead to unnoticed incursions.
As a result, attention has been directed to technological means for surveillance. One possible solution is to place small ground proximity or movement sensors in the region to be surveyed, and to radio to a human-attended center when movement is detected. One disadvantage of this is that some of the sensors might have to be placed on the sovereign territory of another, which might not be possible. In addition, deploying such sensors over many miles along, and over suitable depth of, a border will be quite expensive. Not all the terrain to be protected will be amenable to use of a single type of proximity sensor, so multiple types might be required. Also, such sensors have the disadvantage that battery power would be required, and the changing of batteries in a large plurality of sensors scattered over a region in turn requires substantial manpower. Even if ground proximity sensors were to be deployed, they tend to be susceptible to false alarms such as animal movement (or even to movement of tree roots along the northern border). Historically, ground proximity sensors have been poor performers.
A radar system can survey a region which includes sovereign territory of another, and can provide a current location and speed of an object, and the data can be stored to provide a track (history of locations). Ground Surveillance Radar (GSR) has a long history of use for surveillance, and so constitutes a mature technology. Some of these radars are easy to set up or install using trained personnel. Moving target detection for radar is well known, and can detect objects moving with some radial velocities relative to the radar. Ground surveillance radar (GSR) that is available for border surveillance provides a two-dimensional detection capability, which is to say that it only identifies the location of an object by range and azimuth. Additionally, the GSRs available for border surveillance tend to have slow update rates (half a minute to more than a minute per scan), and also limitations in detection of objects with low radial velocity (relative to the radar location). The two dimensional object location, together with the slow update rate, make radar data somewhat difficult to use for the important task of cueing narrow field of view interrogation cameras to closely observe the target of interest. In addition, significant limitations to angular resolution and range accuracy result in the detection mode of operation not being as effective as the tracking modes. Additional limitations of radar border surveillance include possible inability to detect objects through vegetation and under various clutter conditions. A major disadvantage of radar systems is that they cannot, in general, identify an object. For example, a moving object smaller than a vehicle might be a human intruder, or it might be an animal. Indeed, a low-flying bird might give rise to concern, since radar generally cannot determine the shape of an object. Radar systems undesirably tend to require skilled operators and maintenance personnel.
Cameras can also be used for surveillance. Cameras, like radar systems, have the advantage of being able to extend their sensing capabilities across borders. As with GSR, cameras can be installed and set up by relatively unskilled personnel. They also cost less than radar systems. Cameras have the advantage of being capable of reporting the shape of an object within their fields of view, so can, in principle, tell the difference between an animal and a human. In addition, a video surveillance approach allows for use of infrared (IR) technology to detect warm bodies moving through vegetation and other similar obstructions, as the warm bodies provide enough of a difference between pixels for detection by video analytics. On the other hand, cameras have a problem similar to that of radar, in that they provide only a two-dimensional (azimuth and elevation) representation of a three-dimensional world. Another disadvantage of cameras for surveillance use is that the camera can only “see” objects which subtend a substantial portion of the field-of-view. That is, if the object is small and at a significant distance from the camera, its image may be so small as to be indistinguishable from the background. If a zoom lens function is directed toward the object so as to effectively enlarge the object in the field of view, the field of view is narrowed so that other targets or objects may be able to move through the region without being imaged. Yet a further disadvantage of cameras for surveillance is that the video analytics processing, which is well-known processing for detecting motion from frame-to-frame variations in each pixel, tends to require the operator to configure each individual field of view to be monitored so that detected objects can be converted to geospatial coordinates. This configuration task might take several hours, depending on the operator. Because of this setup time, COTS video analytics products are primarily useful at fixed installations, and tend to be left in position (not moved) once they are set up.
Improved or alternative surveillance arrangements are desired.